Vacuum skin packaging is a process in wide commercial use today which involves placing a perishable food inside a plastic film package and then, removing air from inside the package so that the packaging material remains in close contact with the product surfaces after sealing. Vacuum skin packaging is useful for packaging food and non-food items, and especially desirable in packaging of fresh or frozen meats, such as beef, chicken, pork, and fish. The vacuum skin packaging process itself is now well known in the art. Various vacuum skin packaging processes are disclosed in, e.g., U.S. Pat. No. RE30,009 to Perdue et al.; U.S. Pat. No. 4,055,672 to Hirsch et al.; U.S. Pat. No. 4,375,851 to Paulos; U.S. Pat. No. 5,033,253 to Havens et al.; and U.S. Pat. No. 5,460,269 to Bayer, which are each incorporated herein by reference in their entireties. For example, U.S. Pat. No. RE30,009 to Perdue et al. describe several methods by which a vacuum skin package may be constructed by use of a vacuum chamber. Exemplary of these methods is a process which includes placing an article onto a thermoplastic bottom web or support substrate in a vacuum chamber and then, shaping the top web into a concavity by differential air pressure. While maintaining the concave shape by differential air pressure, the top web is heated to its softening and forming temperature while positioning the web over the article and bottom substrate. A vacuum is drawn in the chamber in a manner such that a vacuum exists between the top web and a bottom support substrate. At this point, the top web is moved to contact the article and the bottom substrate. The top web is thus sealed against the bottom substrate. Typically, the top web becomes a skin on the article and bottom substrate in the finished package, making the finished package difficult to open by the consumer or end user. Consequently, when it is desired to remove the product, a knife or other sharp implements must be used to puncture the packaging film.
Also, well known in the art are easy-open packages and packaging materials in their construction. Reference may be made, for example, to U.S. Pat. No. RE37,171 to Busche et al. which describe an easy open package to be heat-seal closed and peelably reopened. The patent discloses an interior film layer of an adhesive (or tie layers) which may be peelably bonded to either an adjacent exterior film layer or an adjacent interior film layer. Peelability may be provided by adhesive (or tie layers) compositions which include polybutylene in combination with a polyethylene or ethylene/vinyl acetate copolymer.
U.S. Patent Application No. 2005/0042468 to Peiffer et al. disclose a coextruded, biaxially oriented polyester film suitable for use as a lid with trays made of polyester. These films comprise a base layer and a heat-sealable, peelable top layer. The peelable top sealant layer includes a mixture of at least two polymeric-component resins: a polyester and a polyester-incompatible polymer.
U.S. Pat. No. 6,630,237 to Rivett et al. also disclose peelable heat-seal films useful for easy-open packaging applications. The peelable layer of these films includes a blend of polybutylene, ionomer and an ethylene/unsaturated ester copolymer. The patent further discloses a peelable package formed from these films and require that the peelable layer be heat-sealed to itself or a similar film composition in order to provide peelable packages.
U.S. Pat. No. 5,346,735 to Logan et al. describe a film structure useful for vacuum skin packaging comprising a two-ply structure which comprises both an oxygen-impermeable film and an oxygen-permeable film. The two films delaminate at their interface rather than between a support substrate and one of either film. The peelable interface is formed by bonding a layer comprising ethylene/vinyl alcohol copolymer or polyamide of the impermeable film to an adjacent layer comprising ethylene/alpha olefin copolymer of the permeable film.
U.S. Pat. No. 4,859,514 to Friedrich et al. disclose thermoplastic films for easily opened packages which include a first film having a first sealant layer and a second film having a second sealant layer wherein the two sealant layers are heat-sealed together. The first sealant layer may comprise either ionomer or a blend of an ionomer and ethylene/vinyl acetate copolymer, and the second sealant layer may include a blend of ethylene/vinyl acetate copolymer, ethylene/butene copolymer and polypropylene. The first film may separate from the second film at the interface between the two sealant layers.
Notwithstanding the aforementioned advances in the packaging industry, there still remains a need in the art for improved vacuum skin packages which provide the benefits of peelability.